A gripper of the kind mentioned above is disclosed in the Danish patent application No. 1683/83 or U.S. Pat. No. 4,615,374 (Persson). In this previously known gripper, the two gripping jaws are operated by mechanically separate mechanisms, each driven by its own hydraulic cylinder. Although this previously known gripper has proved satisfactory in many respects, it suffers from two distinct disadvantages, i.e.
(a) that two separate hydraulic cylinders are required to perform what is in essence one single operation, i.e. moving the gripping jaws from the position of rest to the gripping position or vice versa, and
(b) that special hydraulic control measures are required to prevent the two jaws colliding with each other during the movements mentioned, especially during the movement away from the gripping position.